1. Field of the Invention (Technical Field)
The present invention relates to apparatuses and methods for in-process sensing of materials transported through roller-based conveyor systems.
2. Background Art
Many manufacturing processes require processing of bulk materials in belt form, ranging from thin sheets of plastics to synthetic polymers with embedded steel wires. These materials are often transported over roller-based conveyor systems to permit a continuous processing stream from station to station.
Processing such bulk materials involves cutting, layering, bonding, and lamination steps which require precise knowledge of the belt position in real-time. However, there are few sensors currently available for monitoring material position during transportation on a conveyor system. The space above the conveyor is typically occupied by processing equipment and is unavailable. In addition, the conveyor environment is often dirty, contaminated with oil, smoky, and subject to extremes in temperature. This harsh environment severely restricts the type of sensors which may be profitably used.
However, significant improvements in product quality and waste minimization can potentially be achieved through the use of on-line belt position sensing. For example, a process at one manufacturer involves positioning a 1" wide "gum strip" at the edge of a wide belt. If the gum strip extends over the edge, the piece (belt plus gum strip) must be scrapped. Because the current manual positioning system is inaccurate, the process specifies a nominal 1/4" safety margin. This margin reduces the incidence of scrapped belts, but results in reduced quality material.
The present invention addresses this problem by permitting real-time monitoring of the belt position during transportation over a conveyor system. Acquiring this information permits closed loop control of processing systems based upon the measured belt position. The sensing roller described herein can immediately benefit presently installed manufacturing equipment. The manufacturing process described above, for example, contains mechanical guides which can modify the gum strip placement based upon electrical command inputs. The position information collected by the sensing roller can be coupled to these command inputs to provide closed-loop control of gum strip placement.
There are no known general purpose systems in place for monitoring the edges of conveyor-transported dielectric materials, the edges of laminated structures such as the gum strip/belt assembly, or measuring the position of wires within layers of dielectric. Researchers have experimented with a vision-based system for monitoring the position of a belt as it moves down a conveyor. Such systems function poorly due to the variations of the reflectivity and color of the material, as well as the factory lighting. In addition, a vision-based system must occupy space above the conveyor, and is subject to error due to smoke, airborne oils, and contamination of optical surfaces.
U.S. Pat. No. 4,623,835, entitled "Web Thickness Sensor Using Loop-Gap Resonator", to Mehdizadeh, et al., discloses a device for measuring the capacitance between a conductive roller and an externally mounted electrode to determine the thickness of a dielectric material. The apparatus required the presence of a conductor on the top side of the belt material being processed. The present invention eliminates this requirement by placing both electrodes on the roller itself.
U.S. Pat. No. 4,968,947, entitled "Apparatus for the Non-Destructive Measurement of the Ohmic Resistance of Thin Layers", to Thorn, measures the ohmic resistance of thin layers of conductive material on the top side of a belt of dielectric material. Again, this apparatus requires the presence of a conductor on the top side of the belt material.
The sensing roller of the present invention permits measuring the 1) thickness profile of the bulk material, 2) the location of material edges, and 3) the position and orientation of conductive wires within belts. The sensor is integrated into the roller used for transport of the material and does not occupy premium space above the conveyor. The sensing roller can be made from rugged materials currently used in rollers and can be incorporated into existing conveyor systems. These characteristics will permit application of closed-loop process control in many demanding applications.